In the fabrication of metal components, it is often necessary to join two previously produced pieces together. This may be the case, for example, where one part is formed by milling while the other is formed by forging. It also occurs when the two parts have different finishes, such as one that is nitride or bead-blasted and one that is chromed. Whatever the case, when a permanent joint between metal parts is needed, welding is often employed. In general, a welded joint tends to be stronger and more resilient that joints made by mechanical fasteners such as screws, bolts, or rivets.
Although many welding techniques have been developed and used throughout the years, friction welding fulfills a unique role. Friction welding is solid-state welding process that induces plasticity in the metals being joined via heat generated by mechanical friction between the pieces. In general, friction welding is accomplished by interfacing a spinning component to a stationary one to generate heat at the interface, and then forcing the pieces together when plasticity occurs in the parts. This fuses the materials. Although friction welding may be viewed as a form of forging by some, the term “welding” herein is used to denote a process by which two metals are permanently joined in a process wherein material at the joint is at sufficient temperature and pressure to produce metal flash at the joint.
As will be appreciated, friction welding provides numerous benefits. Total joining times as low as a few seconds make friction welding a time-efficient technique. Moreover, the use of friction rather than direct heat means that very little of the metal volume beyond the weld interface is affected, and the fact that little or no full melting occurs means that grain growth and other melt-related issues can be largely avoided. Yet another advantage of friction welding is that it can be used to weld materials of very different types, where a wide difference in melting points precludes the use of traditional welding techniques. Examples of welds where friction welding is required include the welding of aluminum to high-strength steel, steel to copper, aluminum alloy to high-nickel-alloy materials and others.
During friction welding, some amount of plastic metal is forced out of the joint during the final forcing phase to create “flash,” which is later removed. While the production of flash may beneficially remove surface impurities from the joint volume itself, the hardened flash can also cause problems in the final welded product. During spin welding where the stationary part is generally cylindrical, the flash forms a flash ring at or just slightly displaced from the level of the joint. Once the weld itself is complete, the welded item is turned as a whole, e.g., in a lathe, and a cutting tool is progressively applied to slowly remove the spinning flash.
Unfortunately, the flash ring sometimes breaks from the part during turning, but remains as a ragged ring of metal hung on the spinning part. When this happens, the flash ring can quickly scour the surface of the spinning part and destroy any precision finish that may have existed there. This is especially troublesome and costly when the part is chromed or otherwise finely finished, and in some cases may result in the need to scrap the entire welded assembly. Thus, while friction welding has many benefits, the occurrence of loose flash rings in this manner has the potential to significantly counteract the efficiency and economy of materials that might otherwise be enjoyed via friction welding.
It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as a reference to prior art nor as an indication that any of the indicated problems were themselves appreciated in the art.